The present invention is directed to air bearing slider designs in hard disk drives. More specifically, the present invention pertains to a configuration for a subambient pressure air bearing slider utilizing negative pressure grooves.
FIG. 1 illustrates a hard disk drive design typical in the art. Hard disk drives 100 are common information storage devices consisting essentially of a series of rotatable disks 104 that are accessed by magnetic reading and writing elements. These data transferring elements, commonly known as transducers, are typically carried by and embedded in a slider body 110 that is held in a close relative position over discrete data tracks formed on a disk to permit a read or write operation to be carried out. In order to properly position the transducer with respect to the disk surface, an air bearing surface (ABS) formed on the slider body 110 experiences a fluid air flow that provides sufficient lift force to “fly” the slider 110 (and transducer) above the disk data tracks. The high speed rotation of a magnetic disk 104 generates a stream of air flow or wind along its surface in a direction substantially parallel to the tangential velocity of the disk. The air flow cooperates with the ABS of the slider body 110 which enables the slider to fly above the spinning disk. In effect, the suspended slider 110 is physically separated from the disk surface 104 through this self-actuating air bearing. The ABS of a slider 110 is generally configured on the slider surface facing the rotating disk 104 (see below), and greatly influences its ability to fly over the disk under various conditions.
FIG. 2 illustrates a typical design for an air bearing surface (ABS) on a slider. Some of the major objectives in ABS 202 designs are to fly the slider 210 and its accompanying transducer 204 as close as possible to the surface of the rotating disk (not shown), and to uniformly maintain that constant close distance regardless of variable flying conditions. The height or separation gap between the transducer 204 of the air bearing slider 210 and the spinning magnetic disk is commonly defined as the flying height. In general, the mounted transducer or read/write element 204 flies only approximately a few micro-inches above the surface of the rotating disk. The flying height of the slider 210 is viewed as one of the most critical parameters affecting the magnetic disk reading and recording capabilities of a mounted read/write element 204. For example, there are many advantages for reducing or having a relatively small flying height. A relatively small flying height allows the transducer 204 to achieve greater resolution between different data bit locations and magnetic fields emanating from closely defined regions on the disk surface. Also, a low flying slider 210 is known to provide improved high density recording or storage capacity of magnetic disks which is usually limited by the distance between the transducer and the magnetic media. Narrow separation gaps permit shorter wavelength signals to be recorded or read as a result. At the same time, with the increasing popularity of lightweight and compact notebook type computers that utilize relatively small yet powerful disk drives, the need for a progressively smaller slider body 210 with a lower flying height has continually grown.
It has also been observed that a constant flying height provides desirable benefits which may be more readily achieved through particular ABS 202 designs. Fluctuations in flying height are known to adversely affect the resolution and the data transfer capabilities of the accompanying transducer or read/write element 204. The amplitude of the signal being recorded or read does not vary as much when the flying height is relatively constant. Additionally, changes in flying height may result in unintended contact between the slider assembly and the magnetic rotating disk. Sliders 210 are generally considered to be either direct contacting, pseudo-contacting or flying sliders which is descriptive of their intended contact with a rotating disk. Regardless of the type of slider, it is often desirable to avoid unnecessary contact with the surface of the spinning magnetic disk so as to reduce the wear on both the slider body and the disk. The deterioration or wear of the recording media may lead to the loss of recorded data, while slider 210 wear may also result in the ultimate failure of the transducer or magnetic element 204.
What often causes changes to the flying height is the continual high-speed movement of the slider 210 across the rotating disk while performing read or write operations. For example, depending on the radial position of the slider 210, the respective linear velocity of the disk varies. Higher velocities are observed at the outer edge of the rotating disk, while lower velocities are found at the inner edge. As a result, the air bearing slider 210 flies at different relative speeds at different radial positions relative to the disk. Because sliders typically fly higher at higher velocities, there is a tendency for flying heights to increase when positioned above the outer regions of the disk. At the same time, lower velocities at the inner regions of the disk cause the slider 210 to fly lower. Accordingly, slider 210 designs must account for the noticeable effect that variations in radial position, and relative velocity, have on the flying height.
The flying height of a slider 210 is also adversely affected by changes in skew. The skew angle is defined and measured as the angle formed between the longitudinal axis of the slider 210 body and the direction of the air flow tangential to the disk rotation. When the mounted slider 210 is positioned near the inner or outer edges of the spinning disk, its longitudinal axis is often skewed in relation to the direction of the air flow. The longitudinal axis of the slider 210 may be defined as a center line of reference running along the length of the slider body. These angular orientations or skew angles typically vary as a rotary actuator arm and gimbal suspension assembly turns about its pivot point thereby moving the slider in an arcuate path across the rotating disk. In view of the growing demand for compact disk drives having relatively smaller actuator arms, larger skew angles are ever more present because of the shortened arm length. It has often been observed that at skew values above zero, sliders are pressurized at reduced values which cause an undesirable decrease in flying height. Even a relatively moderate skew angle range adversely affects the flying capabilities of a slider 210. As a result, ABS designs continually attempt to minimize slider sensitivity to changes in skew.
Another fluctuation in flying height may be identified as slider roll. The roll angle is measured and defined by the difference in flying height between the longitudinal sides of the slider. Whenever a slider flies at skew with respect to the direction of the air flow, an unequal pressure distribution tends to occur between the ABS and the disk. This imbalance causes slider roll where one side of the slider body is closer to the disk surface than the other side. A slider, however, is preferably positioned at a constant slider roll regardless of any changes in the flying conditions including differences in tangential velocity between the inner and outer tracks of the rotating disk, and continuous lateral movement above the surface of the disk or varying skew angles.
Various designs exist for the ABS 202 of sliders 210. For example, as shown in FIG. 2a, in a common catamaran slider, a pair of parallel rails 220 are formed on the slider body 210 that extend along the outer edges of the slider surface facing the disk. Other ABS configurations with various surface areas and geometries have also been developed, such as the design illustrated in FIG. 2b. Rails 220 and other formations typically run along at least a portion of the slider body length from the leading edge 206 to the trailing edge 208. The leading edge 206 is defined as the edge of the slider 210 that the rotating disk passes before running the length of the slider 210 towards a trailing edge 208. The leading edge 206 may be tapered despite the large undesirable tolerance typically associated with this machining process. The transducer or magnetic element 204 is typically mounted at some location along the trailing edge 208 of the slider 210. The rails 220 form an air bearing surface on which the slider flies, and provide the necessary lift upon contact with the air flow created by the spinning disk. As the disk rotates, the generated wind or air flow runs along underneath, and in between, the catamaran slider rails 220. As the air flow passes beneath the rails 220, the air pressure between the rails 220 and the disk increases thereby providing positive pressurization and lift. Catamaran sliders generally create a sufficient amount of lift, or positive load force, to cause the slider to fly at appropriate heights above the rotating disk. In the absence of the rails 220, the large surface area of the slider body would produce an excessively large air bearing surface area. In general, as the air bearing surface area increases, the amount of lift created is also increased. Without rails 220, the slider would therefore fly too far from the rotating disk thereby foregoing all of the described benefits of having a low flying height. A flexible gimbal often provides the slider 210 with multiple degrees of freedom such as vertical spacing, or pitch angle and roll angle which describe the flying height of the slider.
Although simple catamaran sliders are initially effective in providing an adequate flying height, they are especially sensitive to varying skew angle ranges and other adverse flying conditions. When the skew angle is increased, such as when the flying slider moves across the rotating disk, the air pressure distribution beneath the rails 220 may become distorted. By accessing both inner and outer portions of a disk at relatively high speed, air is introduced in an uneven amount under each rail 220 which typically causes slider roll. As a result, the slider 210 experiences an uneven distribution of pressure which may cause the slider to roll in one direction such that the flying height is not uniform between the ABS rails 210. The mounted transducer 204 may therefore be unable to operate effectively or accurately perform its data transfer operations. Regardless of the sensitivity of the ABS rails 220 to various skew ranges and other adverse flying conditions, this rail design is widely acknowledged as a general configuration that provides effective pressurization or lift to enable a slider to fly.
In order to counteract the positive pressurization of the flying slider body to provide a low and constant flying height, it is known to form an ABS that also provides negative or subambient pressurization to pull or draw the slider body towards the disk. For example, negative pressure air bearing (NPAB) or self loading sliders have been known to provide a counteracting negative pressure load. In this dual pressurization scheme, the ABS may be generally formed with a leading edge 206, a trailing edge 208, side rails 220, and one or more cross-rails 222 that extend between the side rails 220. The cross-rail(s) 222, which are often positioned closer to the leading edge 206 than the trailing edge of the slider, creates a subambient pressure region 224 trailing each cross-rail 222 and in between the side-rails 220. The subambient pressure region 224 creates a negative pressure or load that counteracts the positive pressure generated along the side rail portion of the ABS. This counteraction of negative and positive forces has been known to increase the stability and air bearing stiffness of the slider 210, provide rapid slider take-off, and reduce its sensitivity to variations in conditions such as changing disk velocity and radial movement which cause fluctuations in flying height. The compensating changes in positive and negative pressure, in accordance with the varying velocity between the inner and outer tracks of the disk, contributes to the overall objective of maintaining a substantially constant and steady flying height. However, the offsetting forces created in a subambient pressurization scheme may often present undesirable effects that actually cause variations in flying height. A NPAB slider often exhibits noticeable roll as well, and a reduction in flying height at skewed conditions because of unequal pressurization or distribution of air beneath the rails.
All of the aforementioned ABS configurations and modifications for air bearing sliders attempt to achieve a low and constant flying height. Different degrees of effectiveness are provided by these ABS designs which overall do not control flying height, or pitch and roll angles very well. For example, many existing ABS designs have been observed to exhibit an extremely increased slider roll angle over outer tracks regions of a disk. These configurations also typically fail to control the increase in slider pitch angle when moving from inner track to the outer track regions. Thus, there exists a need for an ABS configuration for an air bearing slider that effectively maintains constant flying height and controls roll angle to achieve a greater “stiffness” to the air bearing regardless of constantly changing flying conditions such as the difference in relative velocity at the outer and inner regions of a disk, the relative positioning of a slider over a rotating disk, and varying skew angles ranges.